Lua 5.1 C API short reference (lists all the calls along with a short description of the parameters) by Ewald Arnold [odt, pdf] (aewald-arnold.de)

Lua 5.1 C API short reference (lists all the calls with even shorter descriptions but also includes the stack layout of the ingoing and outcoming Lua values) by Ewald Arnold [xls, pdf] (aewald-arnold.de)